Environmental and breathing zone samples were analyzed for estradiol- benzoate (50500) and other hormones at the Institute of Animal Behavior in Smith Hall, Rutgers University (SIC-8221), Newark, New Jersey, in September 1981 and February 1982. Temperature and ventilation were measured, and air flow patterns were determined. Concentrations of estradiol-benzoate, measured in September 1981, ranged from nondetectable to 1070 micrograms per cubic meter (microg/m3). Concentrations of the first three floors were 170 to 540microg/m3. The NIOSH recommended standard is what is considered a lowest feasible concentration. A follow up survey in February found no detectable amounts of estradiol-benzoate or other hormones. Ventilation measurements showed a balanced system. No recirculation or movement of exhaust air between floors occurred. Temperature readings were near the optimum comfort range. The author concludes that hormone concentrations in Smith Hall are near background values. Recommendations include limiting access to floors 4 and 5, mixing and handling hormones according to strict guidelines, supplying adequate laboratory ventilation, and periodic monitoring of hormone concentrations.